(a) Field of the Invention
The invention relates to timing relays that provide a delayed contact actuation, and in particular to improvements in a relay movement that cooperates with an electromagnet and a timer to actuate switch contacts. Timing relays are used in electrical motor control circuits and automated manufacturing systems to operate one or more switches with a time delay following energizing or deenergizing of the electromagnet.
(b) Description of the Prior Art
Timing relays may be operated in two modes, "On Delay" and "Off Delay." Some devices can operate in either of these two modes, while other devices operate in but one of the modes. In the on delay mode, the time delay in actuating a set of switch contacts occurs after the energization of the associated electromagnet. In the off delay mode, the time delay occurs upon the deenergization of the electromagnet, so that the return of the delayed action switch contacts to their normal state, either normally open or normally closed, lags movement of the electromagnet. The construction and operation of a basic multimode timing relay are shown and described in Haydu et al, U.S. Pat. No. 3,249,716.
In timing relays as shown in said U.S. Pat. No. 3,249,716, the relay movement that actuates the time delayed switch contacts is responsive to the action of an electromagnet, and also includes a set of levers and other mechanical elements to reset and respond to an advancing member of a timer. The timer may be of the expanding bellows, pneumatic type in which the rate of bellows expansion may be set to provide a control over the time delay period. The advancing member of the timer can be attached to the bellows to move therewith, and the relay movement cooperates with this advancing member to produce the time delayed switch actuation. In such multimode devices, the location of the advancing member relative to certain elements in the relay movement determines the mode of operation, i.e., either on delay or off delay.
The relay movement includes springs that are normally compressed for the purpose of actuating the switch contacts with a rapid movement when the springs are released. Upon energization of the electromagnet, and with the timer member located for on delay operation, the timer member is caused to advance to actuate the relay movement. The relay movement then releases the springs to operate the time delayed switch contacts. When the advanceable timer member is located to operate the relay movement in the off delay mode, a like result is obtained upon a deenergization of the electromagnet. In this structure the actuating springs that open and close the time delayed switch contacts may work against one another, such that one spring is loaded by the unloading of the other spring. It would be desirable to eliminate this opposed relationship between the actuating springs.
Time delay relay movements typically comprise a number of complex levers, catches, springs and other mechanical elements that are subject to wear. They have not achieved an optimum of efficient and effective operation of their parts, and accordingly prior art devices have components and operating motions that can be simplified, and better balanced against one another to obtain improved performance.